Wafer debonding system and method

ABSTRACT

The present disclosure relates to a debonding apparatus. In some embodiments, the debonding apparatus comprises a wafer chuck configured to hold a pair of bonded substrates on a chuck top surface. The debonding apparatus further comprises a pair of separating blades including a first separating blade and a second separating blade placed at edges of the pair of bonded substrates diametrically opposite to each other. The first separating blade has a first thickness that is smaller than a second thickness of the second separating blade. The debonding apparatus further comprises a flex wafer assembly placed above the pair of bonded substrates and configured to pull the pair of bonded substrates upwardly to separate a second substrate from a first substrate of the pair of bonded substrate. By providing unbalanced initial torques on opposite sides of the bonded substrate pair, edge defects and wafer breakage are reduced.

REFERENCE TO RELATED APPLICATIONS

This Application is a Divisional of U.S. application Ser. No.15/613,963, filed on Jun. 5, 2017, which claims priority to U.S.Provisional Application No. 62/427,208, filed on Nov. 29, 2016. Thecontents of the above-referenced Patent Applications are herebyincorporated by reference in their entirety.

BACKGROUND

Integrated chips are fabricated through a plurality of processing steps(e.g., etching steps, lithography steps, deposition steps, etc.) upon asemiconductor wafer (e.g., a silicon wafer), followed by dicing thesemiconductor wafer into separate integrated chips. In order to realizehigher integration, simplify packaging processes, or couple circuits orother components, etc., in some cases two or more wafers are bondedtogether before the dicing step, and circuits are fabricated on bothsides of the wafer after thin down. Wafer level bonding is a promisingtechnology for “More than Moore”, where added value is provided todevices by incorporating functionality that does not necessarily scaleaccording to Moore's Law. Debonding is desired in some cases during thewafer level bonding procedure, and can be used for example to separateone wafer from another, and can be used to rework a substrate whenalignment is out of spec or particulates that fall onto a wafer causeinterface voids, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a perspective view of a wafer debonding system fordebonding a pair of bonded wafers according to some embodiments.

FIG. 2A illustrates a schematic diagram of a wafer debonding method fordebonding a pair of bonded wafers using a pair of separating blades withdifferent thicknesses and a pair of pulling heads with different pullforces according to some embodiments.

FIG. 2B illustrates a schematic diagram of a wafer debonding method fordebonding a pair of bonded wafers using a pair of pulling heads withdifferent pull forces according to some alternative embodiments.

FIG. 2C illustrates a schematic diagram of a wafer debonding method fordebonding a pair of bonded wafers using a pair of separating blades withdifferent thicknesses according to some alternative embodiments.

FIG. 3 illustrates a schematic diagram of a wafer debonding method fordebonding a pair of bonded wafers using a pair of separating blades withdifferent thicknesses according to some embodiments.

FIG. 4A illustrates cross-sectional and top views of a separating bladeof a wafer debonding system shown in FIG. 1, 2, or 3 according to someembodiments.

FIG. 4B illustrates cross-sectional and top views of a separating bladeof a wafer debonding system shown in FIG. 1, 2, or 3 according to somealternative embodiments.

FIGS. 5-11 illustrate a series of cross-sectional views of anapplication a wafer debonding system for debonding a pair of bondedwafers according to some embodiments according to some embodiments.

FIG. 12 illustrates a flow diagram of a wafer debonding method fordebonding a pair of bonded wafers according to some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

There are different kinds of debonding approaches: such as single sidedebonding and double sides debonding. A single side debonding needs alower debonding force F1 because of a higher torque with a longer leverarm to wafer connecting point but has a high risk to induce defects nearwafer edges at the opposite side of debonding start point. A double sidedebonding has a low risk to induce defects near wafer edges, but needshigher pull forces F2 and has a high wafer breakage risk because of thelarge wafer bending strength when initiating the debonding process.

The present disclosure relates to improving apparatus and methods forwafer debonding to reduce edge defects and wafer breakage, and also toreduce debonding pull forces needed. In some embodiments, referring toFIG. 1 for example, a debonding apparatus 100 for debonding a pair ofbonded wafers 102 a, 102 b comprises a wafer chuck 104 configured tohold a first wafer 102 a of the pair of bonded wafers in contact with achuck top surface. A pair of separating blades includes a firstseparating blade 106 a and a second separating blade 106 b that areconfigured to be placed at edges of the pair of bonded wafersdiametrically opposite to each other. A flex wafer assembly 108 includesa first pulling head 110 a and a second pulling head 110 b diametricallyopposite to the first pulling head. The first pulling head 110 a and thesecond pulling head 110 b are configured to be placed above the pair ofbonded wafers and to provide pull forces to hold and move a second wafer102 b of the pair of bonded wafers separated from the first wafer 102 a.By providing the two separating blades 106 a, 106 b with differentthicknesses, and/or providing different pull forces through the pullingheads 110 a, 110 b, initial vertical separating heights between thebonded wafers are different. Thereby bending of the wafer is reducedwhen initiating the debonding process, which reduces a possibility ofwafer breakage (compared to inserting two separating blades with thesame thickness and providing the same pulling force through pullingheads).

FIG. 1 illustrates a perspective view of a wafer debonding system 100for debonding a pair of bonded wafers according to some embodiments. Asshown in FIG. 1, a wafer chuck 104 is provided. The wafer chuck 104 canbe a component of a chuck assembly used for holding wafers in place witha fixture that utilizes a vacuum chuck or some other means ofmechanical, electrical, or magnetic attachment. A pair of wafers 102 canbe placed on the wafer chuck with a first wafer 102 a in contact with achuck top surface. A second wafer 102 b is bonded face-to-face to thefirst wafer 102 a through various bonding techniques including directbonding and indirect bonding, such as silicon fusion bonding, oxidebonding, hybrid bonding, or adhesive bonding using an adhesive layerbetween the first wafer 102 a and the second wafer 102 b. A flex waferassembly 108 is configured to be placed on the top surface of the waferchuck 104 to hold a wafer and provide pull forces. The flex waferassembly 108 may be controlled by a programmable drive motor and isconfigured to hold and move the second wafer 102 b of the pair of bondedwafers separated from the first wafer 102 a. The flex wafer assembly 108may comprise at least two pulling heads, a first pulling head 110 a anda second pulling head 110 b that are placed diametrically opposite toeach other about a central axis of the wafer chuck (and/or about acentral axis of the pair of bonded wafers). The pulling heads 110 a, 110b may be utilized to apply pull forces to the second wafer 102 b and toseparate and remove the second wafer 102 b from the first wafer 102 a.The pulling heads 110 a, 110 b are movable in a direction perpendicularto the wafer surface plane and have adjustable top vacuum cup positions,for example, about 3 cm to about 9 cm above the top surface of thebonded wafer pair 102, depending on applications. In some embodiments,different pull forces may be applied by the pulling heads 110 a, 110 bin order to create a greater initial pull force on one side of the pairof bonded wafers 102 a, 102 b and a smaller initial pull force on theother side of the pair of bonded wafers 102 a, 102 b to provideunbalanced initial torques. The greater initial pull force on thepulling head 110 b results in a debonding propagation wave propagatingquickly to enlarge the debonding torque. The smaller initial pull forceon the pulling head 110 a pulls up the lower side the bonded wafer pair102 to prevent scratches at wafer edges. One vacuum system may be sharedby the first pulling head 110 a and the second pulling head 110 b toapply pull forces. A pair of coil springs 112 a, 112 b may respectivelybe attached to the pulling heads 110 a, 110 b to control the pullforces. In some embodiments, the coil springs 112 a, 112 b may havedifferent spring coefficients, such that a first pull force applied bythe first pulling head 110 a is smaller than a second pull force appliedby the second pulling head 110 b. In some embodiments, the springcoefficients of the coil springs 112 a, 112 b can be in a range of fromabout 1×10² N/m to about 1×10⁵ N/m. In some embodiments, the springcoefficient of the second coil spring 112 b can be 10 to 100 timesgreater than the spring coefficient of the first coil spring 112 a toprovide sufficient pulling force differences. In this way, the pullforces introduced by the first and second pulling heads 110 a, 110 b canbe sufficiently unbalanced to provide unbalanced initial torques onopposite sides of the pair of bonded wafers 102 a, 102 b, therebyenhancing the debonding process.

A pair of separating blades is placed at edges of the pair of bondedwafers 102 diametrically opposite to each other. The pair of separatingblades includes a first separating blade 106 a and a second separatingblade 106 b that are configured to be inserted into a bonding interfaceof the first wafer 102 a and the second wafer 102 b from edges tofacilitate the debonding of the first wafer 102 a and the second wafer102 b. In some embodiments, the first separating blade 106 a has a firstthickness that is smaller than a second thickness of the secondseparating blade 106 b. In some additional embodiments, more than twoseparating blades can be provided and distributed evenly along outeredges of the pair of bonded wafers 102 to separate the pair of bondedwafers 102 to further reduce edge defects. In some further embodiments,a monitoring assembly 114, including sensing devices such as a pair ofthree-dimensional cameras or charge-coupled device cameras, is includedin the wafer debonding system 100, to check the debonding processes andprovide information for further adjustment of the separating blades 106a, 106 b. For example, in some embodiments, the monitoring assembly 114detects separate distance of the first wafer 102 a and the second wafer102 b by taking pictures and processing the taken pictures. Themonitoring assembly may also help to determine how much further theseparating blades 106 a, 106 b ought to be inserted between the firstwafer 102 a and the second wafer 102 b, or whether to increase ordecrease the pulling forces applied by the pulling heads 110 a, 110 b.In some embodiments, the pulling heads 110 a, 110 b continuously assertthe first and second pulling forces as the first and second separatingblades 106 a, 106 b are slidably inserted between the first and secondwafers 102 a, 102 b by an increasing amount until the monitoringassembly 114 detects that the first and second wafers 102 a, 102 b havebeen de-bonded on at least one edge (and/or on both edges). As anexample, a vertical distance of at least one edge between the firstwafer 102 a and the second wafer 102 b is extracted by measuring thetaken pictures of the monitoring assembly 114. The extracted verticaldistance is then compared to a vertical dimension of at least one of theinserted blades 106 a, 106 b to determine the de-boned condition: if thevertical distance between wafers is greater than the vertical dimensionof the inserted blade, the wafers are considered as de-bonded at thatedge. In some alternative embodiments, the de-boned condition isdetermined by a pull target distance. For example, the wafers areconsidered as de-bonded when the pulling heads 110 a, 110 b (and thesecond wafer 102 b that is sucked by the vacuum inside the pullingheads) move up a distance greater than 15 mm. In some furtherembodiments, a force sensor is attached to the pulling heads 110 a, 110b to help to determine the de-bonded condition. For example, the wafersare considered as de-bonded when the force sensor detects a zero valueof the pulling forces. One or more of above approaches may be adopted tohelp determine or confirm the de-boned condition. When this de-bondedcondition of the first and second wafers is detected, the first andsecond separating blades 106 a, 106 b can be retracted, and the firstand second wafers, now de-bonded (separated) from each other, can beremoved from the chuck, and another pair of bonded wafers can be placedon the chuck for de-bonding. It is understood that though a pair ofbonded wafers, the first wafer 102 a and the second wafer 102 b, isdescribed above and will continue to be described below forunderstanding how the wafer debonding system 100 works, the workpiece ofthe wafer debonding system 100 includes any suitable substrates for thefabrication of integrated circuits, such as thin slices of semiconductormaterial (such as a crystalline silicon, or a binary compound (e.g.,GaAs wafer), a ternary compound substrate (e.g., AlGaAs), or higherorder compound, etc.), or non-semiconductor materials such as oxide insilicon-on-insulator (SOI), partial SOI, polysilicon, amorphous silicon,or organic materials, among others. Such substrates can have variesdevices or structures fabricated or bonded thereon.

FIG. 2A illustrates a schematic diagram of a wafer debonding method fordebonding a pair of bonded wafers according to some embodiments. Asshown in FIG. 2A, a pair of bonded wafers 102 a, 102 b can be separatedby using a pair of separating blades 106 a, 106 b having differentthicknesses and inserted therebetween from edges of the pair of bondedwafers 102 a, 102 b, and/or by using a pair of pulling heads 110 a, 110b configured to provide different pulling forces and placed above thebonded wafers 102 a, 102 b to pull away one of the bonded wafers 102 bwhile fixing the other of the bonded wafers 102 a on the wafer chuck104. In some embodiments, the pair of separating blades 106 a, 106 b isarranged diametrically opposite to each other. The pair of pulling heads110 a, 110 b can also be arranged diametrically opposite to each other.A first pull point distance 11 from the first pulling head 110 a to acentral axis or center point 200 of the pair of bonded wafers 102 a, 102b can be equal to a second pull point distance 12 from the pulling head110 b to the center point 200 of the pair of bonded wafers 102 a, 102 b.The pair of pulling heads 110 a, 110 b can be placed on top surfaces ofthe second wafer 102 b around places that are within edges of the waferchuck 104 for initial ducking of pulling heads 110 a, 110 b on thesecond wafer 102 b. In some further embodiments, the placement of thepair of pulling heads 110 a, 110 b can be adjusted for variousapplications, in order to improve the debonding quality. The adjustmentmay be based on the information provided by the monitoring assembly 114disclosed in FIG. 1. For example, the pair of pulling heads 110 a, 110 bcan be placed between the edges of wafers 102 a, 102 b and the waferchuck 104. The location of the pair of pulling heads 110 a, 110 b istunable closer or away from the center point 200 of the pair of bondedwafers 102 a, 102 b. The monitoring assembly 114 may check the debondingprocesses and provide information for further adjustment of the locationof the pair of pulling heads 110 a, 110 b and the pulling forces appliedby the pulling heads 110 a, 110 b. In some embodiments, the pullingheads 110 a, 110 b continuously assert the first and second pullingforces as the first and second separating blades 106 a, 106 b areslidably inserted between the first and second wafers 102 a, 102 b by anincreasing or decreasing amount until the monitoring assembly 114detects that the first and second wafers 102 a, 102 b have beende-bonded on at least one edge (and/or on both edges).

FIG. 2B and FIG. 2C illustrate alternative embodiments of schematicdiagrams of a wafer debonding method of FIG. 2A. As shown in FIG. 2B, apair of bonded wafers 102 a, 102 b can be separated by using a pair ofpulling heads 110 a, 110 b placed above the bonded wafers 102 a, 102 bwith different pull forces and a pair of separating blades 106 a, 106 binserted therebetween from edges of the pair of bonded wafers 102 a, 102b with the same thickness. As shown in FIG. 2C, a pair of bonded wafers102 a, 102 b can be separated by using a pair of separating blades 106a, 106 b inserted therebetween from edges of the pair of bonded wafers102 a, 102 b with different thicknesses and a pair of pulling heads 110a, 110 b placed above the bonded wafers 102 a, 102 b with the pullforce. Other features of FIG. 2B and FIG. 2C are similar to FIG. 2A andcan be referred above.

FIG. 3 illustrates a schematic diagram of a wafer debonding method 300for debonding a pair of bonded wafers using a pair of separating bladeswith different thicknesses according to some embodiments. Somedimensions of the wafer debonding method of FIG. 2A are furtherillustrated in FIG. 3. As shown in FIG. 3, the first separating blade106 a has a first length L1, a first thickness T1, and is insertedbetween the first wafer 102 a and second wafer 102 b to a first distancec1 during a debonding process. The second separating blade 106 b has asecond length L2, a second thickness T2, and is inserted between thefirst wafer 102 a and second wafer 102 b to a second distance c2 duringthe same debonding process. The second distance c2 may be equal to thefirst distance c1. The second thickness T2 may be greater than (1.2 to 3times greater preferably) to the first thickness T1. The firstseparating blade 106 a has a first pointed end with a first flare angleα1 and the second separating blade 106 b has a second pointed end with asecond flare angle α2. The second flare angle α2 is equal or greaterthan the first flare angle α1. By providing the two separating blades106 a, 106 b with different flare angles, different distances ofseparation between the wafers are generated when inserting the twoseparating blades into an interface of the bonded wafers. Thereby alarger initial torque is provided on one side of the pair of bondedwafer 102 a, 102 b to enhance debonding wave propagation and reducedebonding force, and a smaller wafer bending is introduced on the otherside of the pair of bonded wafers 102 a, 102 b to reduce the possibilityof wafer breakage but still pulling up the wafer edges to preventscratches or other edge defects.

The pair of bonded wafers 102 a, 102 b has a maximum diameter D, and isplaced on the wafer chuck 104 and is concentric to the wafer chuck 104during the debonding process. The wafer chuck 104 has a diameter D′ (orgreatest lateral dimension if not a round shape) smaller than themaximum diameter D of the pair of bonded wafers 102 a, 102 b. In somepreferred embodiments, the diameter D′ of the wafer chuck 104 can beabout 0.5 to about 0.9 times of the maximum diameter D of the pair ofbonded wafers 102 a, 102 b, such that the pair of bonded wafers 102 a,102 b has desired spaces (free-standing area) to perform the debondingprocess and also has desired back support from the wafer chuck 104. Forexample, the pair of bonded wafers 102 a, 102 b can be 12-inch (i.e. 300mm) wafers before dicing and packaging, and the wafer chuck 104 ispreferred to have the diameter D′ in a range of from about 150 mm(millimeter) to about 250 mm. Correspondingly, the first thickness T1 ofthe first separating blade 106 a can be in a range of from about 2 mm toabout 6 mm, and the second thickness T2 of the second separating blade106 b can be also in a range of from about 2 mm to about 6 mm, butgreater than the first thickness T1. A ratio of the first thickness tothe second thickness T1:T2 can be in a range of about 1:1.2 to 1:3. Insome embodiments, the lengths L1, L2 are equal. The first distance c1inserted by the first separating blade 106 a and the second distance c2inserted by the second separating blade 106 b can respectively be in arange of from about 8 mm to about 12 mm. The pair of pulling heads 110a, 110 b is arranged diametrically opposite to each other. In somefurther embodiments, some more pulling heads, such as 110 c, 110 d, and110 e can also be placed on top surfaces of the second wafer 102 b forpulling up the second wafer 102 b. The multiple pulling heads aredistributed in a certain pattern. For example, the multiple pullingheads can be arranged in a linear line that passes through the centralaxis of the second wafer 102 b and/or evenly spaced one from another,and the pulling forces provided by the multiple pulling heads can belinearly or parabolic increased, in order to collectively provideenhanced pulling forces. Using the setups disclosed above, initialdebonding lengths of two sides of the pair of bonded wafers 102 a, 102 bare unbalanced, i.e., a first initial debonding length d1 introduced bythe first separating blade 106 a and corresponding pulling forces issmaller than a second initial debonding length d2 introduced by thesecond separating blade 106 b and corresponding pulling forces.Comparing to the single side debonding method, the debonding methodsdisclosed above are less likely to introduce wafer edge defects.Compared to the balanced double side debonding method, the new debondingmethods disclosed above need smaller pull forces, and are also lesslikely to cause wafer breakage.

FIG. 4A illustrates cross-sectional and top views of a separating blade400 a of a wafer debonding system shown in FIG. 1, FIG. 2, or FIG. 3according to some embodiments. It is appreciated that the separatingblade 400 a can be the first separating blade 106 a and the secondseparating blade 106 b shown in FIG. 1, FIG. 2, or FIG. 3. Theseparating blade 400 a may have a rounded front wedge as shown in thetop view located at an upper portion of FIG. 4 to reduce scratch risk.The separating blade 400 a may have a pointed end as shown in thecross-sectional view located at a lower portion of FIG. 4. As anexample, the separating blade 400 a can be designed to have a width W ina range of from about 6 mm to about 14 mm, a thickness T in a range offrom about 2 mm to about 6 mm, and a pointed end length L in a range offrom about 6 mm to about 14 mm. The separating blade 400 a can be madeof a material with a small hardness to reduce scratch risk, and a highYoung's modulus to create initial bonding area. The scratch hardness ofthe separating blade 400 a can be smaller than that of the material ofwafers to be processed (e.g. wafers 102 a, 102 b in FIG. 3). The scratchhardness of the separating blade 400 a can be smaller than about 5gigapascals (GPa) when the wafers to be processed is made of silicon,and Young's modulus of the separating blade 400 a can be greater thanabout 3 gigapascals (GPa). For example, the separating blade 400 a canbe made of polyetheretherketone (PEEK) with a scratch hardness in arange of from about 0.05 GPa to about 0.3 GPa, and a Young's modulus ina range of from about 3.76 GPa to 3.95 GPa, or other materials with suchrequirements of Young's modulus and hardness in some embodiments. FIG.4B illustrates a top view of a separating blade 400 b of a waferdebonding system shown in FIG. 1, FIG. 2 or FIG. 3 according to somealternative embodiments. As an alternative option of the rounded frontwedge of the separating blade 400 a of FIG. 4A, the separating blade 400b may have a quarter-circular wedge corresponding to a wafer edge of abonded wafer pair 102. The separating blade 400 b may be respectivelyplaced at opposite sides of the wafers to be processed matching thecircumferences of the wafers and corresponding to the separating blades106 a, 106 b of FIG. 1, FIG. 2 or FIG. 3, and may have inserted lengthL1, L2 and thicknesses T1 and T2 (T1, T2 are in the directionperpendicular to the top view plane shown in FIG. 4B). The insertedlength L1, L2 and the thicknesses T1 and T2 may have similarrelationships and ranges as described in FIG. 3. The debonding area isenlarged (as shown by dashed line) by using the separating blade 400 b,and the crack risk is thereby reduced.

FIGS. 5-11 illustrate a series of cross-sectional views of anapplication to form a three-dimensional integrated circuit using a waferdebonding system for debonding a pair of bonded wafers according to someembodiments according to some embodiments.

As shown in cross-sectional view 500 of FIG. 5, a first wafer 502 isprepared. In some embodiments, the first wafer 502 comprises a siliconsubstrate. In other embodiments, the first wafer 502 comprises asubstrate including germanium, gallium arsenic, or other suitablesemiconductor material. The first wafer 502 may be a device wafer andprocessed to form features, such as circuits, connecting layers,contacts and other applicable structures. Though not shown in FIG. 5, insome embodiments, an adhesive layer can be formed on the first wafer 502to facilitate a bonding process to be performed. The adhesive layer canbe a spin-on adhesive or an alternative adhesive layer, such as alaminated tape, wax, or other suitable material can be used.

As shown in cross-sectional view 600 of FIG. 6, a second wafer 602 isprepared. In some embodiments, the second wafer 602 can be device wafer.The second wafer 602 may comprise a silicon substrate or othersemiconductor substrate similar to the first wafer 502. In some otherembodiments, the second wafer 602 can be a carrier wafer, and comprise asapphire substrate, or a substrate made of thermoplastic polymer, oxide,carbide, or other suitable material. In some embodiments, an adhesionpromoter layer (not shown) may be spun on the second wafer 602 tofacilitate the bonding with the first wafer 502 of FIG. 5 in asubsequent step.

As shown in cross-sectional view 700 of FIG. 7, the second wafer 602 isbonded to the first wafer 502 to form a bonded wafer pair. The secondwafer 602 and the first wafer 502 may be bonded through direct orindirect bonding techniques, such as a fusion silicon bonding process,an oxide bonding process, a hybrid bonding process, through the adhesivelayer 504, or other applicable techniques. A thermal and/or cure processmay be performed to facilitate the bonding process. In some cases, thebonding process may be imperfect: a misalignment may occur where thefirst wafer 502 and the second wafer 602 are shifted from each otherwhen bonded, some impurity particles or voids may be formed at thebonding interface, among other imperfection bonding occasions. After thebonding process, a wafer bonding condition is determined by a monitoringor measurement process, such as generating and processing bondingcondition images taken by a monitoring system (e.g. the monitoringassembly 114 shown in FIG. 1) or some measurement to check electricalconnections between the first wafer 502 and the second wafer 602. Themethods of the present invention may be implemented in association withvarious types of monitoring or measurement components and systems, andany such system or group of components, either hardware and/or software,incorporating such a method is contemplated as falling within the scopeof the present invention. The monitoring process, for example, can berealized by applying a pad probe or optical scan over the wafer surface.In some embodiments, the bonding alignment and interface voidsconditions are detected. It may be determined that whether themisalignment and/or the interface voids are in the desired regions. Adecision is then made accordingly regarding whether a debonding processshown in FIG. 8 is needed. Such a decision can be made manually or usinga pre-set computer program.

As shown in cross-sectional view 800 of FIG. 8, if the decision is madethat a debonding process is needed, the second wafer 602 is thendebonded and separated from the first wafer 502. The debonding processcan be performed using the debonding system and methods disclosed inthis application. A pair of separating blades 106 a, 106 b withdifferent thicknesses or flare angles and/or a pair of pulling heads 110a, 110 b with different pull forces can be utilized to facilitate thedebonding process with fewer edge defects and/or reduced wafer breakage.

As shown in cross-sectional view 900 of FIG. 9, if the debonding processis performed as shown in FIG. 8, the second wafer 602 is re-bonded tothe first wafer 502 similar to the process shown in FIG. 7. In someembodiments, the debonded first wafer 502 and second wafer 602 areinspected for surface defects before the re-bonding process. Accordingto the inspection result, the first wafer 502 and the second wafer 602may be replaced, cleaned, or re-polished to prepare for the re-bondingprocess. Then, a wafer bonding condition determination process, andfollowing debonding and re-bonding process similar as described abovefor FIG. 7 and FIG. 8 may be repeated.

As shown in cross-sectional view 1000 of FIG. 10, additional processes,such as thinning, planarizing, forming circuit features, and any otherprocessing steps can be performed to the first wafer 502 or the secondwafer 602. In some embodiments, a third wafer 1002 can be bonded to thebonded wafer pair of the first wafer 502 and the second wafer 602. Then,a wafer bonding condition determination process, and following debondingand re-bonding process similar as described above for FIG. 7 and FIG. 8may be repeated.

As shown in cross-sectional view 1100 of FIG. 11, the wafer stack of thefirst wafer 502, the second wafer 602, and the third wafer 1002 aredebonded if the decision is made that a debonding process is needed. Thedebonding process can be performed using the debonding system andmethods disclosed in this application. A pair of separating blades 106a, 106 b with different thicknesses or flare angles and/or a pair ofpulling heads 110 a, 110 b with different pull forces can be utilized tofacilitate the debonding process with fewer edge defects and/or reducedwafer breakage.

FIG. 12 shows some embodiments of a flow diagram of a wafer debondingmethod for debonding a pair of bonded wafers according to someembodiments. Although method 1200 is described in relation to FIGS.5-11, it will be appreciated that the method 1200 is not limited to suchstructures disclosed in FIGS. 5-11, but instead may stand aloneindependent of the structures disclosed in FIGS. 5-11. Similarly, itwill be appreciated that the structures disclosed in FIGS. 5-11 are notlimited to the method 1200, but instead may stand alone as structuresindependent of the method 1200. Also, while disclosed methods (e.g.,method 1200) are illustrated and described below as a series ofoperations or events, it will be appreciated that the illustratedordering of such operations or events is not to be interpreted in alimiting sense. For example, some operations may occur in differentorders and/or concurrently with other operations or events apart fromthose illustrated and/or described herein. In addition, not allillustrated operations may be required to implement one or more aspectsor embodiments of the description herein. Further, one or more of theoperations depicted herein may be carried out in one or more separateoperations and/or phases.

At operation 1202, a first wafer is prepared. In some embodiments, thefirst wafer is a device wafer. A front side of the first wafer may beprocessed to form features, such as circuits, connecting layers,contacts, and other applicable structures. FIG. 5 illustrates someembodiments of a cross-sectional view 500 corresponding to operation1202.

At operation 1204, a second wafer is prepared. The second wafer isanother device wafer or a carrier wafer that is used to support thefirst wafer during subsequent processes. The second wafer may include asubstrate made of semiconductor, sapphire, thermoplastic polymer, oxide,carbide, or other suitable material. FIG. 6 illustrates some embodimentsof a cross-sectional view 600 corresponding to operation 1204.

At operation 1206, the second wafer is bonded to the first wafer to forma bonded wafer pair. The second wafer and the first wafer may be bondedthrough a fusion bonding process, through an adhesive layer, or otherapplicable techniques. A thermal and/or cure process may be performed tofacilitate the bonding process. At operation 1208, a wafer bondingcondition is determined by a monitoring or measurement process. In someembodiments, it is determined that whether a misalignment and/orinterface voids between the first and second wafers are in the desiredregions. A decision is then made accordingly regarding whether adebonding process is needed. Such a decision can be made manually orusing a pre-set computer program. FIG. 7 illustrates some embodiments ofa cross-sectional view 700 corresponding to operation 1206 and operation1208.

At operation 1210, if the decision is made that a debonding process isneeded, the second wafer is then debonded and separated from the firstwafer. The debonding process can be performed using the debonding systemand methods disclosed in this application. A pair of separating bladeswith different thicknesses or flare angles and/or a pair of pullingheads with different pull forces can be utilized to facilitate thedebonding process with fewer edge defects and/or reduced wafer breakage.At operation 1212, the debonded first wafer and second wafer areinspected for surface defects. At operation 1214, the first wafer andthe second wafer may be replaced, cleaned, or re-polished. FIG. 8illustrates some embodiments of a cross-sectional view 800 correspondingto operation 1210, 1212 and 1214.

At operation 1216, the second wafer is re-bonded to the first wafer.Then, a wafer bonding condition determination process, and followingdebonding and re-bonding process similar as described above may berepeated. FIG. 9 illustrates some embodiments of a cross-sectional view900 corresponding to operation 1216.

Therefore, the present disclosure relates to wafer debonding system andmethod for to reduce edge defects and wafer breakage, and also to reducedebonding pull forces. By providing two pulling heads with differentpulling forces and/or inserting the two separating blades with differentthicknesses into an interface of the bonded wafers, unbalanced initialtorques are provided on opposite sides to enhance debonding wavepropagation and reduce debonding force. The lower pull force at a lowerside can ensure that the lower side of the top wafer can be pulled up inorder to prevent scratch at wafer edges.

In some embodiments, the present disclosure relates to a debondingapparatus. In some embodiments, the debonding apparatus comprises awafer chuck configured to hold a pair of bonded substrates on a chucktop surface. The debonding apparatus further comprises a pair ofseparating blades including a first separating blade and a secondseparating blade placed at edges of the pair of bonded substratesdiametrically opposite to each other. The first separating blade has afirst thickness that is smaller than a second thickness of the secondseparating blade. The debonding apparatus further comprises a flex waferassembly placed above the pair of bonded substrates and configured topull the pair of bonded substrates upwardly to separate a secondsubstrate from a first substrate of the pair of bonded substrate.

In other embodiments, the present disclosure relates to a debondingapparatus. In some embodiments, the debonding apparatus comprises awafer chuck configured to hold and suck a first substrate of the pair ofbonded substrates in contact with a chuck top surface. The debondingapparatus further comprises a pair of separating blades including afirst separating blade and a second separating blade that are configuredto be placed at edges of the pair of bonded substrates diametricallyopposite to each other. The debonding apparatus further comprises a flexwafer assembly comprising a first pulling head and a second pulling headdiametrically opposite to the first pulling head, wherein the firstpulling head and the second pulling head are configured to be placedabove the pair of bonded substrates and to hold and move a secondsubstrate of the pair of bonded substrates separated from the firstsubstrate.

In yet other embodiments, the present disclosure relates to a debondingapparatus for debonding a pair of bonded substrates. The debondingapparatus includes a wafer chuck configured to hold a first substrate ofthe pair of bonded substrates in contact with a chuck top surface, and apair of separating blades including a first separating blade and asecond separating blade that are configured to be placed at edges of thepair of bonded substrates diametrically opposite to each other. Thefirst separating blade has a first thickness that is smaller than asecond thickness of the second separating blade. The debonding apparatusalso includes a flex wafer assembly comprising a first pulling head anda second pulling head diametrically opposite to the first pulling head.The first pulling head and the second pulling head are configured to beplaced above the pair of bonded substrates and to hold and move a secondsubstrate of the pair of bonded substrates separated from the firstsubstrate.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A debonding apparatus for debonding a pair of bonded substrates, comprising: a wafer chuck configured to hold the pair of bonded substrates on a chuck top surface; a pair of separating blades including a first separating blade and a second separating blade placed at edges of the pair of bonded substrates diametrically opposite to each other, wherein the first separating blade has a first thickness that is smaller than a second thickness of the second separating blade; and a flex wafer assembly placed above the pair of bonded substrates and configured to pull the pair of bonded substrates upwardly to separate a second substrate from a first substrate of the pair of bonded substrate.
 2. The debonding apparatus of claim 1, wherein the pair of separating blades is configured to facilitate the separating of the pair of bonded substrate by having the first separating blade inserted between the first substrate and second substrate to a first distance and having the second separating blade inserted between the first substrate and second substrate to a second distance.
 3. The debonding apparatus of claim 2, wherein the second distance is equal to the first distance.
 4. The debonding apparatus of claim 1, wherein the flex wafer assembly comprises a first pulling head and a second pulling head diametrically opposite to the first pulling head.
 5. The debonding apparatus of claim 4, wherein the first pulling head is placed at a first side of the second substrate closer to the first separating blade and the second pulling head is placed at a second side of the second substrate closer to the second separating blade, wherein the first pulling head is configured to apply a first pull force and the second pulling head is configured to apply a second pull force greater than the first pull force.
 6. The debonding apparatus of claim 4, wherein pull forces of the first pulling head and the second pulling head are controlled by a first coil spring and a second coil spring respectively coupled to the first pulling head and the second pulling head, and wherein a second spring coefficient of the second coil spring associated with the second pulling head is at least 10 times greater than that of a first spring coefficient of the first coil spring associated with the first pulling head.
 7. The debonding apparatus of claim 1, wherein the first separating blade and the second separating blade respectively has a rounded front wedge.
 8. The debonding apparatus of claim 1, wherein the first separating blade and the second separating blade respectively has a circular segment wedge that lines a circumference of the bonded substrate.
 9. The debonding apparatus of claim 1, wherein the first separating blade and the second separating blade are made of polyetheretherketone material.
 10. The debonding apparatus of claim 1, wherein a diameter of the wafer chuck is in a range of from about 0.5 to about 0.9 times of a diameter of the pair of bonded substrates.
 11. A debonding apparatus for debonding a pair of bonded substrates, comprising: a wafer chuck configured to hold and suck a first substrate of the pair of bonded substrates in contact with a chuck top surface; a pair of separating blades including a first separating blade and a second separating blade that are configured to be placed at edges of the pair of bonded substrates diametrically opposite to each other; and a flex wafer assembly comprising a first pulling head and a second pulling head diametrically opposite to the first pulling head, wherein the first pulling head and the second pulling head are configured to be placed above the pair of bonded substrates and to hold and move a second substrate of the pair of bonded substrates separated from the first substrate.
 12. The debonding apparatus of claim 11, wherein the first separating blade has a first thickness that is smaller than a second thickness of the second separating blade.
 13. The debonding apparatus of claim 11, wherein the first separating blade is inserted between the first substrate and second substrate to a first distance, and the second separating blade is inserted between the first substrate and second substrate to a second distance that is equal to the first distance.
 14. The debonding apparatus of claim 11, wherein the first pulling head is placed at a first side of the second substrate closer to the first separating blade and the second pulling head is placed at a second side of the second substrate closer to the second substrate separating blade, wherein the first pulling head is configured to apply a first pull force and the second pulling head is configured to apply a second pull force greater than the first pull force.
 15. The debonding apparatus of claim 11, wherein the first separating blade has a pointed end with a first flare angle smaller than a second flare angle of the second separating blade.
 16. A debonding apparatus for debonding a pair of bonded substrates, comprising: a wafer chuck configured to hold and suck a first substrate of the pair of bonded substrates in contact with a chuck top surface; a pair of separating blades including a first separating blade and a second separating blade having different thicknesses and configured to be inserted between the first substrate and a second substrate of the pair of bonded substrate from edges of the pair of bonded substrates diametrically opposite to each other; and a flex wafer assembly comprising a first pulling head and a second pulling head diametrically opposite to the first pulling head, wherein the first pulling head and the second pulling head are configured to be placed above the pair of bonded substrates and to hold and pull the second substrate upward until the flex wafer assembly flexes the second substrate from the first substrate.
 17. The debonding apparatus of claim 16, wherein the first separating blade is inserted between the first substrate and second substrate to a first distance, and the second separating blade is inserted between the first substrate and second substrate to a second distance that is equal to the first distance.
 18. The debonding apparatus of claim 16, wherein the first pulling head is placed at a first side of the second substrate closer to the first separating blade and the second pulling head is placed at a second side of the second substrate closer to the second substrate separating blade, wherein the first pulling head is configured to apply a first pull force and the second pulling head is configured to apply a second pull force greater than the first pull force.
 19. The debonding apparatus of claim 16, wherein the flex wafer assembly has additional pulling heads placed on top surfaces of the second substrate for pulling up the second substrate.
 20. The debonding apparatus of claim 19, wherein the pulling heads are distributed in a linear line that passes through a central axis of the second substrate and/or evenly spaced one from another; and wherein pulling forces provided by the pulling heads are linearly or parabolic increased one from another. 